Solution : https://service.sap.com/sap/support/notes/214563 (SAP Service marketplace login required)
Key words : 
additional key words route, attached source code corrections, redetermine plant/shipping point', sales document processing, dialog box inquiring, shipping point, overview screen, system displays, patch level, solution implement
Related Notes : 
       
| 321021 | Unwanted redetermination of the route | 
| 308245 | Incorrect shipping point on subitem after SH change | 
| 192056 | No route determinatn during change of ship-to party |